Modern mail-handling machines processing unsealed envelopes typically include a moistener for moistening the flap and then sealing the flap before passing on the envelope to a weigher and postage meter. Moisteners typical of the known machines included a moistened water wheel, solid or of wicking material, over which the glue-line side of the flap was passed. Commonly-assigned U.S. Pat. No. 3,911,862 describes a spraying system, wherein a nozzle, moved to follow the flap edge, sparys water on the flap as it passes by the nozzle. As the speed and reliability demands made of such machines increase, such moisteners do not always operate entirely satisfactorily. The spray moistener described in the referenced patent, which essentially sprays water over three large overlapped areas, has the drawback that it is not well applicable to a machine processing a large variety of envelope shapes and sizes, such as Nos. 6, 10 and 15 envelopes. Moreover, the spray nozzle cannot accurately track and be confined to the glue line, but tends to wet flap areas outside of the glue line.
The copending application, Ser. No. 291,095 (C-435) describes an improved moistener comprising a hypodermic needle which under computer control can be caused to follow accurately the glue line at the flap edge as the open-flap envelope passes overhead and to spray a metered amount of water confined to the glue line. For this moistener to operate, the computer must know the flap profile. If known, the computer can readily calculate the positions the spraying needle must occupy in order to confine the sprayed water to the flap glue line. To the best of our knowledge, there are no known apparatus capable of mapping the flap profile of an envelope while the envelope is being transported through a mail handling machine, much less capable of performing this function for envelope transport speeds of up to four per second.